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which condense on the surface or may react chemically with the insulation material . If hygroscopic materials are used , they must be fully protected by an impervious layer / vapour barrier .
Protective coverings and finishes The efficiency and service of insulation is dependant on its protection from moisture entry and mechanical or chemical damage . Choices of jacketing and finishing materials are based on the mechanical , chemical , thermal and moisture conditions of the insulation , as well as cost and appearance . Particular attention should be paid to ultraviolet from sunlight degrading the insulation .
PROTECTIVE COATINGS CAN BE DIVIDED INTO FUNCTIONAL TYPES Weather barriers The basic function of weather barriers is to prevent ingress of water . Applications are usually metal jackets , plastic or coatings of weather barrier mastics .
Vapour barriers These are designed to retard the passage of moisture vapour from the atmosphere to the surface of the insulation . Joints and overlaps must be sealed with vapour tight adhesive or sealer . There are three types of vapour barriers :
• Rigid jacketing ; reinforced plastics ; aluminium or stainless steel fabricated to exact dimensions and sealed vapour tight .
• Membrane jacketing metal foils , laminated foils or treated paper , which are generally factory applied to the insulation .
• Mastic applications , either emulsion or solvent type , which provide a seamless coating , but require time to dry .
Mechanical abuse covering Metal jacketing / cladding provides the strongest protection against mechanical damage from personnel , equipment and machinery . The compressive strength of the insulation should also be taken into consideration when assessing mechanical protection . Low flame spread and corrosion resistant coverings When selecting material for potential fire hazard areas , the insulation and the covering must be considered as a composite unit .
Appearance coverings and finishes Coatings , finishing cements , covers and jackets can be chosen with regards to their appearance in exposed areas .
Hygienic coverings Coatings and jackets must present a smooth surface , which resists fungal and bacterial growth , especially in food processing areas and hospitals .
Thank you for your question , Jannie . I hope that this gives a better understanding of what insulation is about and its application . One special note , when applying insulation ( armorflex ) to small air conditioning system pipework do you use cable ties ? If so , how tight do you pull up the cable ties ? Remember you must not compress the armorflex to more than a maximum of 10 % or the insulation will be compromised .
Thanks to everybody for the overwhelming response . I receive on average , over sixty questions per month and cannot publish all of them . But keep them coming , as I may answer you directly .
Looking forward to hearing from you .
Grant Laidlaw
REFERENCES : 1 . SETA training
Thank you for all for your interesting questions . Send your problems ( and sometimes your creative solutions ) to acra @ netactive . co . za with ‘ Solutions Page ’ in the subject line . You may include pictures . RACA
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RACA Journal I July 2023 www . refrigerationandaircon . co . za